Nested Navigators and Login Flows

The following call looks correct, and yet it does nothing except print an error:

navigation.navigate('Details', { productId: 7 });

The action 'NAVIGATE' with payload {"name":"Details","params":{"productId":7}} was not handled by any navigator.

The Details screen exists, but the call was made from a screen in a different tab, and that tab's stack cannot see it. This happens as soon as navigators are nested, so this lesson starts there. It then adds a login flow, in which state decides which screens exist. Passing data with `params